Your ban system apparently has a gaping hole in it which is not banning intentional feeders fast enough. Please see the attached image. This person has ruined 9 games so far, and these are placement matches for most people at this point. They just ran into turrets over and over without saying anything. After all this time, the system should be able to stop this; there isn't really a good excuse for letting this through.
I am using a view which does not show the summoner name, since you're not allowed to...but I wish I could call this person out: